The present invention relates to a direct current motor including an armature core around which windings are wound as concentrated windings.
A typical direct current motor includes an armature core including a plurality of teeth, and a plurality of windings wound around the teeth. A slot is formed between adjacent teeth. Such a direct current motor includes a type that has windings wound the plurality of teeth as distributed windings and a type that has windings wound around the plurality of teeth as concentrated windings. Each coil is arranged so as to traverse the plurality of slots in the distributed windings, whereas each coil is wound around only one tooth so that it does not traverse the plurality of slots in the concentrated windings. The occupation ratio of a winding in a slot is higher for concentrated windings than for distributed windings.
In lieu of the typical direct current motor, which includes two magnetic poles (magnets) and three slots, a direct current motor including a greater number of magnetic poles and slots has been proposed. For instance, Japanese Laid-Open Patent Publication No. 2004-88915 describes a direct current motor including six magnetic poles, eight slots, and twenty-four commutator segments. A larger number of magnetic poles and slots enables effective use of the magnetic flux. This enables the manufacturing of a further miniaturized and lighter direct current motor.
In a direct current motor as that described above, it is effective to have a large ratio of the constraint torque with respect to the mass of the portion of the motor functioning as a magnetic path (including armature core), that is, the constraint torque/mass ratio, when manufacturing a further miniaturized and lighter motor. However, it would be insufficient just to increase the number of magnetic poles and the number of slots to increase the constraint torque/mass ratio. Further, various specifications other than the number of magnetic poles and the number of slots must be optimized.